1. Field of the Invention
The invention relates generally to storage area network (“SAN”) and more specifically relates to recovering and booting a computer system using a SAN.
2. Discussion of Related Art
To allow for recovery in the event of a disaster, many companies replicate data volumes of a computer server to a disaster recovery site that is remote from the computer server. While the data volumes comprise information for services provided by the computer server, the computer server also uses a boot volume that comprises operating system data and supporting files for booting and running the computer system. Accordingly, many companies also replicate or take a “snapshot” of the boot volume to allow the computer server (or its backup) to boot from a backup copy of the boot volume. However, keeping the snapshot of the boot volume up-to-date can be time consuming and error prone because the boot volume is being actively controlled by the operating system and is also being constantly updated by the administrator and various software.
One partial solution to this initial problem is known as Boot from SAN. Boot from SAN allows the computer server to directly use a logical unit of a SAN as the boot volume. Note that a “SAN” is used broadly and may actually refer to a volume, a logical unit, or a logical unit number of a storage area network. The SAN may be a local SAN, and logical units of the local SAN may then be replicated to a remote SAN at a disaster recovery site. Because the boot volume is actually a logical unit of the local SAN, it may be easier to keep a snapshot of the boot volume up-to-date on the remote SAN. For example, the local SAN rather than the computer server may be responsible to forward a write request to the remote SAN after the local SAN receives the write request from the computer system. However, there remains the problem of allowing the computer server to actually make use of the replicated boot volume on the remote SAN.
More specifically, a host bus adapter of the computer server would have already been configured to boot from the logical unit of the local SAN through a configured path. Meanwhile, multipathing technology is available to allow the computer server to access the logical unit through an alternate path similar to how TCP/IP reroutes network traffic. The multipathing technology is typically implemented in a multipath driver. Although the computer server would be able to access the logical unit whether through the configured path or the alternate path during normal operation with the use of the multipath driver, the multipath driver is not available during an initial boot process. Instead, the host bus adapter would only attempt to boot using the configured path rather than the alternative path during the initial boot process even if the configured path is broken. Additionally, although the multipath driver would also allow the computer server to access another logical unit (e.g., the replicated boot volume on the remote SAN) through another path, the multipath driver is likewise not available during the initial boot process.
Moreover, even if the host bus adapter incorporates certain multipathing capabilities, the host bus adapter is still unable to handle an event in which the host bus adapter is able to access a logical unit but is unable to actually boot from the logical unit. For example, one such event occurs when the configured path to the logical unit is not the currently “active” path in that the logical unit is being managed by a secondary controller.
Thus it is an ongoing challenge to recover and boot a computer server/system using a SAN.